Many of the travel arrangements provided by ABTA Members are protected in case of the financial failure of the travel company. You should, however, always ask your travel company if protection applies to your travel arrangements.
This depends whether your holiday company specifically states in their booking conditions that they can make changes like this. If they don’t reserve the right to do so, then any change will be a breach of contract. If they do reserve the right to make the changes, then they must follow what their booking conditions say.
If the building/renovation work is significant in that the noise and dust levels are high and/or a number of facilities are no longer available, you should speak to your travel rep or travel company and they should be able to provide you with a suitable alternative or upgrade subject to availability.
Hotels have traditionally provided services on the basis of people travelling in pairs, with a limited number of single rooms. Since hotels charge per room, not simply the number of people staying in them, solo travellers will proportionately pay higher prices, though many hotels will offer a discounted rate to solo travellers rather than charging them the full room rate.